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1Gohm // 2.5pF is 63Hz - and that does not include any effects of compensation that may be required or stray capacitance. So you may actually end up around 50Hz.
The LMP7721 has about 12pF input capacitance, so that is 1G // 12pF = 13Hz...which will probably end up around 5-7Hz after compensation.
See the "Compensating for Input Capacitance" section in the "Application Hints" section of the LMC6001 datasheet.
I suppose, your bandwith is basically limited due to the 1GOhm feedback resistor, and not due to the amplifier.
I would reduce the 1GOhm down to 100MOhm, this way I could reach roughly a 10 times higher bandwith. The transimpedance ("gain") of your circuit will also be reduced, but you can compensate it with a second stage, wich is simply a voltage amplifier with a gain of 10. Choose a low offset, low noise opamp for the second stage.
My opinion is, that you can't reach your target by simply changing the amplifiers.
In case you are able to post more details of your circuit (what is is for, what are the requirements, for example), the more help you can get.
